fix(coding-agent): bound refinement drain during disposal and extend session-replacement timeouts

[MingTeer]

Summary

/new (daemon new_session command), /resume (switch_session), and fork can fail on the client with a false 30s timeout while the server is still draining in-flight continual-harness refinement during session disposal. The command actually succeeds server-side a few seconds later.

Fixes #1190.

Changes

• Bound the refinement drain during async disposal with a 15s default budget (AgentSessionDisposeOptions.refineDrainBudgetMs); refinement is best-effort persistence, so abandoning it past the budget is preferable to stalling session replacement past client timeouts.
• Skip starting a due-but-not-yet-started auto-refine for user-initiated session replacement (runDueRefineOnDispose: false), so /new, /resume, and fork never trigger a fresh model call while leaving a session.
• Give new_session, switch_session, and fork a dedicated 120s client timeout instead of the generic 30s default, so a slow-but-healthy replacement never surfaces as a false client-side failure.

Tests

• agent-connection-daemon.test.ts: replacement commands use the dedicated timeout.
• agent-session-runtime.test.ts: session replacement passes runDueRefineOnDispose: false.
• agent-session-serialized-refine.test.ts: drain budget bounds in-flight refinement waits; due refinement is skipped on user-initiated disposal.

Note

Bound refinement drain during session disposal and extend session-replacement timeouts

• Adds a 15s drain budget (DEFAULT_REFINE_DISPOSE_DRAIN_BUDGET_MS) to AgentSession._drainPendingRefinementForDisposal so in-flight refinement cannot block teardown indefinitely; emits a refine-failed error if the budget is exhausted.
• Adds AgentSessionDisposeOptions to let callers skip due auto-refine on disposal; session replacement (via AgentSessionRuntime.teardownCurrent) passes { runDueRefineOnDispose: false } to avoid starting a fresh auto-refine during user-initiated teardown.
• Raises the client-side timeout for new_session, switch_session, and fork requests to 120s (DAEMON_SESSION_REPLACEMENT_TIMEOUT_MS) in DaemonAgentConnection, preventing false 30s timeout errors while the server drains refinement.
• Behavioral Change: disposal that previously waited unboundedly on in-flight refinement now abandons and emits a refine-failed error after 15s (or a caller-supplied budget).

^{Macroscope summarized 50653d4.}